


A Parent's Soul

by Zuza (GreenSpades)



Category: Undertale (Video Game)
Genre: Child Death, Child Frisk, Frisk is an energetic trouble magnet, Gen, Genderless Frisk, Implied/Referenced Child Abuse, Papyrus is no help, Parent Sans (Undertale), Sans Remembers Resets, Sans has a newly appointed "Dad" status, Sans is gonna be worked to the bone
Language: English
Status: In-Progress
Published: 2016-07-27
Updated: 2016-08-14
Packaged: 2018-07-27 04:09:19
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,776
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7602847
Author URL: https://archiveofourown.org/users/GreenSpades/pseuds/Zuza
Summary: <blockquote class="userstuff">
              <p>At the end of a Genocide run, Chara and Frisk's souls are separated. Sans learns the truth about what's been going on, and what he learns changes everything. Whether he likes it or not, his soul has essentially "adopted" Frisk, and now he can't help but view them as his own child- which means, in this RESET, he's going to have to be a little more proactive than usual. But that's fine. He loves the kid, really. He just wishes that the world wasn't out to get them. Oh, and that they'd eat something besides candy for once.</p>
            </blockquote>





	1. Prologue

**Author's Note:**

> Hello hello hello everyone! This is not my first rodeo writing fanfiction, but it IS my first time writing Undertale fanfic. It's also my first time posting on this website. Let's uh, hope I don't screw it up...
> 
> Anyway, this story grew from me wanting to see Sans act as a protective parent towards Frisk, but I just couldn't find enough fanfic to satisfy. You know how it goes: if no one's written what you want to read, write it yourself!
> 
> I'm having fun with this so far, so I'll probably update semi-regularly. Thanks for reading and I hope you enjoy!

He couldn’t understand.

He couldn’t understand!

**H e  j u s t  c o u l d n ’ t  u n d e r s t a n d . . .**

It didn’t make any sense. It went against everything he knew about this… this demon child. How many times had he killed it already? How many times had he given the same bullshit speech? …How many times had the kid fallen for it? It was impossible for them to still be ignorant of his tricks. They knew by now that he could never forgive them. They’d been dunked so many times, he couldn’t even keep track anymore.

So why?

The kid knew all of his attacks leading up to the fake spare. They breezed through them all without losing any HP. But every time Sans “spared” them, they always hit the MERCY button, and they always got dunked on, losing any progress they’d made in the fight. Did they think the pain of death was fun? Were they really that screwed up in the head? Well, they had to be a freak to literally murder everyone in the underground, but he’d thought even they didn’t like to pointlessly die.

Maybe this was all just a trick of theirs. He knew they had a thing for cruelty, what with their sadistic genocidal habits. They liked to stab people in the back. Yes, that had to be it. They were just waiting for him to break- to finally trust them, to spare them for real- all so that they could see the look on his face when THEY dunked HIM.

Well, that wasn’t going to work. He’d caught onto their game, and he wasn’t about to play by their rules.

100 kills later, and Sans wasn’t so sure anymore.

You can’t be locked in repetitious battle with someone for that long and not pick up on a few things. One of the things he’d realized was that… maybe… heck, it sounded insane, even in his own thoughts… but… perhaps… the kid who always pressed the MERCY button, might not be the same kid who came back afterwards looking more pissed than ever. The demon that kept swinging their knife and dodging his attacks had gleaming red eyes so full of hate and determination it made his bones rattle. But the person who wore a soft smile as they futilely spared him time and again, always met his hollow gaze with warm, brown eyes filled with unshed tears.

Maybe he was losing it. Maybe he was so desperate to find some sort of last glimmer of hope that he was hallucinating kindness in a being devoid of goodwill. He didn’t know what to believe anymore. He began to study their soul as they fought, and over the course of the next few rounds he noticed something odd that he’d never seen before. Every time the human’s crimson soul moved, a shadow seemed to cling to it, trailing behind. Souls didn’t have shadows, being a source of light themselves.

So… what…?

And then, Sans was struck with an absurd, desperate idea. If he was wrong, it would kill him. But, really… what did he honestly have left to lose? The way he saw it, he had everything to gain if he succeeded, and if he failed…

Well, he’d get to see Papyrus again.

The kid reloaded and came at him again. Sans went through the normal motions, not betraying a thing. But, when it was time for his usual spiel, he stopped. Finally, he gave in. It was time. Time to end everything, for better or for worse, once and for all. Even though he was utterly terrified and his bones shook and sweat dripped from his skull and his instincts screamed at him to keep fighting… despite it all, Sans felt a wave of sweet relief wash over him.

The torture would be over soon.

“Kid… listen. I’m… I’m gonna take the bait. We’ve done this so many times, I have to believe… you’re honestly trying to be a better a person. So… I guess… Papyrus would be pretty disappointed in me if I didn’t give you that chance.”

The human froze, utter shock written on their dusty face. Sans just kept smiling and spread his arms wide, beckoning them in for a hug.

“C’mere, pal.”

***Sans is sparing the human.**

An internal war was clearly displayed in the human’s frantically changing expressions. Rage, joy, desperation, longing… Sans couldn’t read them all. The human’s eyes flickered between red and brown as they shuffled back and forth. They’d take a step towards him and then take an abrupt step back, as if fighting with themselves over which route to take. The MERCY button shone.

Gathering himself, Sans reached out not only with his arms but with his entire being. His pale blue soul manifested from his rib cage and thrummed gently as it called for the person that once upon a timeline he KNEW he’d been friends with…

_Buddy…_

_Frisk…_

_Please, come back to me!_

***The human remembers something.**

Frisk was filled with DETERMINATION like never before as they surged forward and…

The two human souls tore apart.

One, a horrible, malformed and oozing black thing returned to the human’s body. The other, a brilliant and cheeky red, shot for Sans like a missile. Before Sans had the opportunity to react, their souls merged.

_In a sudden flood that threatened to overwhelm him, all of his memories from the previous timeline were returned. Where before Sans had only managed to recall bits and pieces, now it was like remembering yesterday._

_He remembered Frisk, and everything that had happened the first time they fell into the Underground. He remembered how they befriended everyone on their journey, and how they were determined like no other. They were his little buddy, the kind human who always showed mercy. The last thing he remembered before the world RESET was leaving Frisk alone in the Judgement Hall after wishing them luck against Asgore._

_But as great as it was to have his own memories back, it still didn’t explain why the world RESET, or why Frisk came back not as themselves. The red soul joined with his own felt a pang of distress. Frisk was filled with a desperate need for Sans to see and understand- to know the truth. So, with a rush of determination, they shared their own memories._

_Sans watched with growing horror as Frisk was killed again and again and again and again, often in extremely brutal ways. Asgore, Undyne, Muffet, Mettaton… they’d murdered the kid enough times to give even Sans a run for his money. He’d known Frisk was merciful, but the fact that they endured this torture and STILL refused to fight back was nothing short of mind-blowing. And to think that they forgave and befriended everyone after getting past them… this kid had to be a saint._

_But no matter how kind Frisk was, the fact remained that they were still a child, and they were still hurting, and they remembered being killed vividly. Fear began to take root, and every time they were forced to reload a SAVE point, that fear grew. After dying by Asgore’s hand over 20 times, their determination began to falter._

_That’s when the demon saw its chance._

_“Greetings,”_ _it said, when Frisk encountered it for the first time in the loading screen. “I am Chara. I have been your constant companion throughout your journey… and now, it is time for me to help you.”_

_“Help me how?” Frisk had asked, sounding very small and scared._

_“I know you’re frightened. But that’s okay. I know a way to make you brave. I know a way to make you so strong, no one will ever be able to hurt you again. That’s what you want, right? To stop hurting? To go home? Just trust me, and I’ll be able to keep you safe.”_

_But Frisk still didn’t trust it. Something about this entity reminded them of Flowey._

_“How would you keep me safe?_

_”Simple. I’ll help you gain LOVE.”_

_All at once, Frisk understood, and they were sickened at the very idea._

_“What do you say, partner?”_ _The demon held out its hand._

_“No! I don’t want this!”_

_The demon’s face twists into a horrible grin that Sans recognizes as the same expression the human wore when his brother was cut down._

_“Well, that’s just too bad. After all… SINCE WHEN WERE YOU THE ONE IN CONTROL?”_

_The demon lunged. There was the flash of a knife, a searing pain, and then… Frisk was trapped within their own mind._

_The world RESET and poor Frisk was forced to watch as all of their friends were slaughtered by their own hands. Chara controlled their body like a puppet, but every time Frisk was hit, every time they died…. That pain was felt by Frisk and Frisk alone._

The world snapped back into focus.

Trembling, Sans looked up from the soul he’d just absorbed and met the furious gaze of Chara. The only soul left in Frisk’s body was the demon- which meant that there was nothing left to stop them as they raised their knife and slammed the FIGHT button.

Fury and guilt crushed him like a tidal wave as Sans felt his magic build with a strength and intensity so great it physically hurt to hold it back.

“So…” his voice wavered, but then his entire demeanor hardened as he stood tall and stared down the creature that had stolen everything from him.

“You’re the person I shoulda been dunking this whole time.”

“That’s right…” Chara smirked. “All you’ve managed to do is murder a little kid over and over. I hope you’re proud of yourself.”

“I think I’ve had enough of you,” Sans snarled, even as he flinched at the cruel truth of the demon's words.

Chara lunged forward and brought their knife down.

The roar of firing Gaster Blasters filled the Judgement Hall for the last time.

The world RESET.


	2. A New Chance

**Notes for the Chapter:**

> Hello everyone! I'm so sorry about the wait. It took longer than I wanted to post this chapter, but I didn't want to upload anything that I felt was less than my best. I had to scrap what I had written and redo the entire chapter at one point, because I felt like I needed to find a completely different approach. Anyway, I hope you all enjoy this latest development in the story, and thank you very much to all of my wonderful readers for your comments and support!

Eyes flying open, Sans gasped and clutched at his chest. Panic blurred his mind as he tumbled out of his unmade bed and scrambled in the tangled sheets. A phantom pain pierced his rib cage, tracing the path that a sharpened knife had cut. He’d moved too slowly, the Blasters fired just an instant too late-

The room was dark and quiet. The soft blue light of his magic gently illuminated the peaceful surroundings, and Sans went completely still as he let the comforting familiarity of his home wash over him. Taking slow, deep breaths, Sans managed to calm himself down. The magic faded from his eye and his bedroom was plunged back into pitch blackness.

Alright.

He had to think rationally.

There had obviously been a RESET. Chara would not have done it, and the flower couldn’t, so that meant, somehow, Frisk had gathered the determination to do it themselves. Sans had never been so grateful for a RESET. This was a second chance for a happy ending, and it meant that everyone… was… alive…

Suddenly, Sans was moving faster than he’d ever moved before in his life. He got to his feet, crossed the room, flung the door open, and rushed down the hallway to his brother’s bedroom practically at the speed of light. It was only when he reached Papyrus’s door that he balked.

Was this real? What if he opened the door to find the room empty? Could he bear it, if this was all just a cruel trick and his brother was still dead and dust? He hardly dared, but…

But he had to see.

Slowly, with a trembling hand, Sans cracked the door open and peeked inside. For a terrible instant, there was only darkness. But then his eyes adjusted and he saw a familiar shape, resting in that old race car bed. He began to weep.

“Sans? What are you doing out of bed? It’s the middle of the night…”

“Papyrus?” his voice wavered as he spoke, and his soul flickered with a desperate, rising hope.

“Yes, brother?” Papyrus responded, voice losing the sleepy edge as he became more alert. “What is wrong? Are you crying?”

Papyrus’s right eye lit with orange magic as the taller skeleton sat up in bed, and in the light he observed Sans standing in the doorway. Sans had wrapped his arms around himself, shaking like a leaf in the wind as he looked at Papyrus with an unreadable expression.

“Did you have a nightmare?” Papyrus whispered, although he already knew the answer.

“Yeah,” Sans answered hoarsely. He wiped at his eyes in a fruitless effort to stop the tears and met his brother’s concerned gaze, smilingly softly. “It was a nightmare.”

Papyrus reached a decision.

“Come here, brother,” Papyrus instructed sternly. Sans cautiously did so, only to get abruptly swept up into a giant bear hug and pulled into bed alongside Papyrus.  
“It is obvious you are in dire need of a cure for nightmares, and the greatest cure of all is my company! Don’t worry- I, the Great Papyrus, will happily guard you and keep you safe from all bad thoughts!”

The dam broke.

Sans buried his face in the blankets to muffle his sobs. Papyrus just sat there, patiently holding him until he could catch his breath and the tears gradually subsided.

“Heh… th-thanks, bro…”

“It is no trouble! Goodnight, Sans.”

“…Goodnight.”

The next morning came all too soon.

Papyrus was up bright and early as usual, but Sans lingered in bed. He wasn’t in a hurry to move, either. He was content simply to hear the sounds of his brother, alive and well, bustling about in the kitchen preparing breakfast. For once, everything was alright, and for the first time in a long time, Sans had hope.

“SANS! YOU LAZYBONES!”

Yep, it was good to be home.

But of course, Sans’s peace of mind could not last. Shortly after finally dragging himself out of bed and picking at the breakfast spaghetti Papyrus had made, he was hit out of the blue by a sudden, awful realization.

If the world had RESET… was Chara back in Frisk’s body? Would Sans be forced to watch as everyone he knew and loved was killed all over again? …Would he be forced to…? His memories summoned unbidden the image of Frisk’s small, battered, and fragile body impaled on multiple blood-spattered bones-

Struck with an abrupt wave of nausea, Sans had to fight to keep Papyrus’s already unappetizing spaghetti from making a second appearance. Fear chilled him to the bone, and he tugged his coat tighter around himself. Papyrus continued to prattle on about puzzles and humans, seemingly oblivious to his brother’s distress.

“-AND THEN WE NEED TO REPORT TO UNDYNE- SANS! ARE YOU EVEN LISTENING TO ME?”

“Huh? Oh, yeah bro. Sorry, I uh… zoned out there for a second.”

Papyrus leveled him with a scrutinizing gaze.

“…Are you alright?” the taller skeleton asked in a lowered voice.

“I don’t know yet,” Sans said honestly. He was too tired to lie. “But I’m going to find out.”

“Hmm…” Papyrus considered this. “I know something is wrong, but… I won’t force it from you if you don’t wish to speak about it. I just hope that one day you’ll come to trust me.”

“Paps! Paps, I trust you. I trust you more than anyone, but… I need to deal with something first, okay?”

“…Alright,” Papyrus conceded with a sigh. “Do what you must, brother.”

Permanent smile morphing into a genuine one, Sans couldn’t hide his relief. “Thanks, bro. You’re the best.”

And just like that, full volume was restored.

“NYEH-HEH-HEH! OF COURSE I AM! BUT ALTHOUGH I HAVE GIVEN YOU THE FREEDOM TO DO WHAT YOU LIKE TODAY, I STILL EXPECT YOUR PUZZLES TO BE RECALLIBRATED!”

“You got it.”

Not long after, Sans began the long trek to the Ruin doors, snow crunching beneath his feet. Technically, he could use a shortcut, but he was so emotionally and magically drained he didn’t want to risk it. Also, he’d be lying if he said he didn’t want to simply enjoy the sights and sounds of a life-filled Underground. He could only pray that things would stay this way.

As he finally stood in front of the shut doors, Sans felt the icy grip of anxiety slowly strengthening its hold. In a jumble of guilt, fear, and hope, his mind turned over the various possibilities of what could happen when the human child finally left the Ruins. In the worst case scenario, the human would come out covered in dust and wearing Chara’s gleeful smile. Once upon a time, Sans would have had a simple solution to that. He would’ve blasted the kid where they stood, over and over and over again until they ran out of determination or gave up. But he was not the same Sans of previous RESETS. Now, Sans had no idea what he would do. He knew now that not only was Frisk completely innocent, but that they and they alone would be the one to bear the pain of **every- single- blow.**

He didn’t know if he could ever bring himself to deliver one of those blows.

But even if Frisk came out dust-free, Sans would still be in trouble of a different kind. He would be facing the small child he’d promised to protect. The child he’d all but abandoned to die time after time as they traversed the Underground. The child he himself brutally murdered more times than he could count.

And most devastatingly of all, the kid would remember everything.

God, what was he supposed to do? He would beg for forgiveness, but all the apologies and hot dogs and jokes in the world could never reverse the damage.

Heh, it was funny, now that he thought about it- the pure futility of everything.

Time itself, even after rewinding, couldn’t undo the damage.

So what chance did he stand?

Well, chance or no chance, the only thing he could do for now was wait. Leaning his back against a tree next to the Ruin doors, Sans stifled a yawn. Frisk could emerge from the doors at any moment, and when that happened he had to be ready for whatever fate would bring.

The minutes passed.

The minutes became hours.

The morning gave way to noon, and there was still no sign of any human.

Despite his best efforts, Sans had dozed off a couple of times, but now he couldn’t sleep if he tried. Yet more worries had been added to his plate. Frisk had not taken this long in either of the previous RESETS. They should be out of the Ruins and well on their way through Snowdin by now. As the time slowly ticked by, Sans began to fret.

What was going on?

Was Chara toying with him?

…Was Frisk okay? Had they been hurt, or trapped somehow?

He began to pace back and forth in front of the doors. He ignored his phone when it buzzed. When Papyrus came looking for him and suspiciously inquired as to way he was guarding the Ruins, Sans said simply that he wanted to watch for humans somewhere other than his sentry station. He claimed that the old spot was too boring and a change of scenery was long overdue. Papyrus was not convinced, but decided to let him be.

Much, much later, Papyrus returned to find that Sans was no longer pacing, but still had not ventured away from the Ruin doors in all that time. Normally, Papyrus would have been thrilled to see his brother being vigilant about a job, but _this_ was borderline ridiculous.

“Brother, what are you waiting for?” Papyrus asked in a sharp voice, hands on his hips.

“A human,” Sans responded shortly.

“Tell me honestly!”

“I am being honest. What’s your problem? I’m doin’ my job aren’t I? Shouldn’t you be proud or whatever?” Sans’s voice was the sullenest Papyrus had ever heard it.

“Sans, your shift ended many hours ago! It is almost time to go home and eat dinner- and you STILL haven’t recalibrated your puzzles!”

“Woah, really?” Sans looked genuinely surprised. “Damn. Uh, sorry bro. I’m gonna have to take a rain check on your dinner spaghetti.”

“Why?” Papyrus challenged.

“Because… I… because!” Sans turned away, his inward conflict written clearly on his face. It was so very tempting to go with Papyrus, to quit his self-assigned guard duty. But what if Frisk came while he was gone? That would leave the poor kid to navigate their way to Snowdin all by themselves, and the ground was so icy and treacherous, especially now that it was getting dark, and the temperature was falling and he knew humans needed to stay warm…

“You’re worrying me, Sans. You’re not acting like yourself!”

“I have to wait for them, bro,” Sans mumbled, half to himself. The shorter skeleton looked at the Ruin doors, and then at Papyrus, only he wasn’t really looking at Papyrus, but rather through him.

“I have to wait,” he repeated, eye sockets vacant. As his fear grew and twisted with guilt, something inside of him finally snapped, and the words became a mantra.

“I have to wait. I have to wait, I have to-“

“Sans?”

“I have to wait, I can’t abandon them, not this time, I have to wait!”

“Sans!”

“I have to wait, I have to wait, I-“

“SANS!”

His mind cleared, and he found himself trembling violently, and when had he started clawing at his own face? Papyrus was gripping his shoulders in panic. Tears were streaming from the taller skeleton’s eyes, and that’s when Sans realized he was crying too.

“…Sans?”

“Paps, I… I think I’m losing it,” Sans admitted quietly. He gave dry, humorless laugh. “Heh… it’s… finally driven me over the edge.”

Papyrus engulfed him in a hug.

“You’re going to be okay, Sans,” Papyrus’s voice wavered. “I could sense your magic, just now, and it felt… sick. Like your soul is hurting, deeply. But, it’s going to be okay. If there’s a problem with your soul, I know Dr. Alphys can help!”

“I don’t know about that…”

“Nonsense!” Papyrus said desperately. “We’re going to help you Sans, with whatever is wrong. And I’m going to start by getting you home. Come on-“

“NO!” Sans jerked away as a fresh wave of anxiety clutched his soul. “I can’t leave, I have to…”

Papyrus studied him carefully.

“Is this something you really have to do?” the younger brother asked.

“Yes! Yes, it is.”

“…Then, I will stand guard with you.”


End file.
